Comment on New fuel cell could enable electric aviation
xthexder@l.sw0.com 5 days ago
They’re comparing it to lithium batteries for power density, but ignoring that the sodium metal in this case is a consumable, unlike batteries.
They say it’s 1200 Wh / kg of sodium, however gasoline is a whole 3800 Wh / kg, and somehow I think the carbon dioxide is less harmful than the same amount of sodium hydroxide. Not to mention how much more complicated storing liquid sodium would be since it reacts with air.
1200 Wh / kg of sodium
That is about the H2 energy release from sodium reacting with water (perhaps just humidity in air).
however gasoline is a whole 3800 Wh / kg
H2 has 33000wh/kg, and so if you were starting with sodium, might as well pour water on it on the ground, and fill the plane up with automatic high pressure H2.
There are no emissions other than water vapour from the sodium process because the reaction leaves solid byproducts other than H2.
From what the article says, this fuel cell produces sodium oxide by reacting sodium with oxygen. There’s no hydrogen gas being produced in the fuel cell.
The emissions are sodium hydroxide, or sodium carbonate after it reacts with carbon in the air.
(Also now I’m not sure where I got 1200Wh/kg from. The article says both 1000 and 1500 Wh/kg)
Article says whole system is 1000wh/kg (including support machinery). There are 5 (including intermediate step) reactions of air and sodium. I’d guess they are using 100% humidity air. H2 is part of the reaction with humidity, and is a much more rapid and “exothermic” reaction than transformation to SaO.
muusemuuse@lemm.ee 5 days ago
So that might not be a big deal. Most of the energy in gasoline is released as heat and not useable.
Natanael@infosec.pub 5 days ago
Not sure it’s enough.
Airplane engines are about 35% efficient. Maybe you can push it upwards 50% with state of the art designs.
Fuel cells hits about 60-70%, state of the art can maybe hit 85% (and the electric engines can be efficient enough to be part of the error margin in this equation). Best case you’re halving wasted energy. That means you need AT LEAST half the energy density, or else you’re carrying more fuel mass for the same flight. Might be tolerable if it is at least cheaper, but you’re also adding stress and wear as you do.